Heterogeneous catalysts, including inorganic nanoparticles supported on carbon, are widely used to increase the rates of many chemical reactions. For small scale applications typical of research or development environments, catalysts are often provided in the form of a fine powder to provide maximum surface area. Catalyst powders are then added to a liquid containing the reactants. Once the reaction is complete, the catalyst must be separated from the solution, typically by filtration. When performing reactions at larger scales, such as in industrial settings, catalysts are often provided in the form of a fixed bed of particles or pellets. In these cases, reactions are typically performed as the reactants flow over or though the fixed bed. For example, the fixed bed is then contacted with the fluid reactants, with the reaction proceeding while the fluid is in contact with the catalyst. After an appropriate time in contact with the fixed catalyst bed, the fluid, which now contains the product of the chemical reaction, continues on for further processing.
Despite the wide use of heterogeneous catalysts in both industrial and research settings, existing catalysts suffer from a number of shortcomings; among these are inefficient use of precious metals, limited life time, and a tendency to be pyrophoric in contact with air. For research and development environments, the need to carry out a filtration step can be disadvantageous, particularly in the case of finely divided and/or pyrophoric catalysts. For larger scale applications in which a fluid containing the reactants flows over a fixed catalyst bed, the transport of the fluid through the catalyst bed can limit the rate of the reaction, and require larger pumps because of the pressure drop through the catalyst bed. Further, unwanted reactions can produce high molecular weight products which clog the pore spaces within and between the catalysts decreasing the activity of the catalyst, and the effective lifetime of the catalyst.